the relationship between president obama and africa as a whole, but especially south africa because as you've been talking about, his friendship with nelson mandela. very profound. and you could feel it, this place lit one cheers and excitement as soon as the cameras showed president obama had arrived. he will speak as a singular honor, having been invited to speak. they only met that one time. but really there are -- they are brothers in arms in a struggle that nelson mandela began and advanced and continues. >> that greeting there, that was the secretary general, ban ki-moon, taking the podium. only one meeting. president obama in south africa months ago as nelson mandela was ailing at home chose ton visit at that time. did go to robben island on that visit. brought his daughters to robben island, as well. kind of a pilgrimage for nelson mandela. ban ki-moon speaking on behalf of the united nations. of course the american presidents in the crowd, president obama, president bush, president carter among the more than 90 world leaders who have gathered in south africa this morning to ce